how did I miss this?

[kochanie]

for years, I've been reading about the big bang, seeing the images, whatever... when did they start measuring length with time (sorry...just can't seem to come to grips with this :)

'But what’s most remarkable about this blob is its size: It's 55,000 light-years long, which is comparable to the radius of the disk-shaped Milky Way.'

Comments

[snej]

A light-year is a unit of distance - it's the distance light travels in a year. (About ten trillion kilometers, says Wikipedia.) It's sort of like saying "Los Angeles is eight hours from San Francisco", only more precise because light has a constant speed and cars don't.

Most of our distance units are based on actual distances in the world around us - cubits and so forth. (The meter was originally declared as a ten-millionth of the distance from the equator to the North Pole.) Even in the solar system we use "astronomical units" or AUs, which are the distance from the Earth to the Sun (about 93 million miles.) But distances to stars are so huge that there's nothing we can base them on that makes intuitive sense; and worse, we don't know the distance to anything outside the solar system exactly enough to use it as a reference. So they fell back on time-based units like the light-year, which we do know exactly.

[Not an astronomer, but my wife used to be one, and I picked up a buncha stuff...]

[kochanie]

Everything you say in these posts makes logical sense, and I can picture it, but at the same time, my mind still kind of breaks on this point. Maybe they way they wrote, the deeper we look, the further back. There's something very confounding there - as you mentioned lots we don't know or understand.

[snej]

I love how, when we look out/back as far as we can, we see the Big Bang itself as a final glowing curtain behind everything.

(And it's a good thing, too. There was a problem called Olber's Paradox that pointed out that, if the universe were infinite, then no matter what direction you looked in, your line of sight would eventually hit a star. Which would mean that the entire sky would be lit up as bright as the sun, and we'd be fried. The Big Bang theory finally explained why this doesn't happen.)

(Oh, and the reason the glowing curtain doesn't fry us is that, because the universe is expanding, that light's been Doppler-shifted way, way down the spectrum like a receding ambulance. So it ends up as very low-energy microwaves instead of the original gamma rays. Luckily for us.)

[kochanie]

Ah, but near this same article, it said somethng about maybe being able to glimpse the moments before the big bang... where does it end?? ;)